Not applicable.
This invention relates to the incorporation of fire retardant treatments into wood composite products such as oriented strand board, medium density fiberboard, fiber board and particle board. The invention also relates to the method of manufacturing wood based composite products whereby fire retardant compositions are added to the wood furnish prior to drying, forming and pressing into a finished board or panel product. (A xe2x80x9cwood furnishxe2x80x9d is defined as wood strands, chips, particles, flakes or fibers. xe2x80x9cWood particlesxe2x80x9d are defined broadly in this specification to include webs of splintered wood formed by twisting or crushing billets of wood, as well as other forms of wood particles.) The invention further relates to the products made by these processes.
The production of wood based composite panel products has increased dramatically in recent years. Oriented strand board (OSB) production exceeded that of plywood in 2000. In order to continue this new growth, additional uses for OSB need to be developed. Composite wood products find application in the construction of residential housing and commercial buildings. Common applications for these products include roof sheathing, wall sheathing, flooring, structural insulated panels and engineered wood components such as I-joists. With the ever expanding production capacity of wood based composites there is a critical need to find additional uses. One such possibility is for structural and non-structural building components to be made resistant to fire. However, by virtue of their lignocellulosic composition, wood based composites are inherently susceptible to combustion.
Chemical preservatives and fire retardant treatments are readily available for solid lumber and plywood. Such chemical treatments are applied to lumber and plywood using vacuum pressure processes to ensure uniform distribution of the active ingredients throughout the wood components thereby guaranteeing optimum performance.
Historically, attempts to incorporate chemical treatments into wood based composites using similar technology have failed for economic reasons or more commonly because of technical problems associated with irreversible and excessive swelling of the treated panels and severe loss of structural integrity.
The development of an economically viable fire retardant treatment for wood based composites with minimal negative or no impact on board structural properties, would be desirable to the industry and consumer as whole.
The incorporation of a wood preservative in aqueous form directly into green wood particles, without first drying the wood particles, is disclosed in U.S. Ser. No. 09/550,027, filed Apr. 14, 2000.
One aspect of the invention is a method of forming a fire-retardant wood-based composite. The method includes the steps of providing a green wood furnish and treating the green wood furnish with an amount of a phosphate/borate fire retardant treatment effective to increase the fire retardancy of the resulting wood-based composite, compared to the fire retardancy of the corresponding wood-based composite lacking the fire retardant. The treated green wood furnish optionally is dried to a moisture content suitable for fabrication of the wood-based composite. The treated green wood furnish is blended with a binder and then bound, as by pressing the furnish, to form a fire-retardant wood based composite.
Another aspect of the invention is the product formed according to the preceding process.
One advantage of the present invention is that the aqueously applied fire retardant is not easily leached out of the composite board after treatment. This result is surprising. The fire retardant may also act as a catalyst to cure the binder and thus promote binding; this is also surprising. Also, the addition of the fire retardant in aqueous form to green wood chips, without the need to dry them to a low moisture content first, is believed to be novel, and saves the energy which would otherwise be expended by drying the green wood chips before treatment, then applying the aqueous fire retardant (and also rewetting the chips), and finally drying the chips a second time.